The failure of a computer system (e.g., a desktop computer, a laptop) may be recovered by restoring the operating system or a part of the BIOS (Basic Input/Output System) which is corrupted. If the corruption is at the operating system level, the recovery may be performed from a backup partition on the hard disk. For example, the BIOS boots from an alternative partition and restores the main boot partition.
In some severe cases where the entire hard disk or a part of the BIOS has been corrupted (and thus the hard disk is not accessible), recovery may be done using an external storage device, such as, for example, a CD-ROM or a Flash drive. Users must have physical possession of the storage device. The situation may be more difficult if a user is traveling or if the storage device has been misplaced. In additional, system recovery professionals may have to support a wide variety of systems. It is very inconvenient for them to carry a lot of storage drives to cater for different computer systems.